Download Over-the-Air (DLOTA), provided by the Browser & Content Download DRM workgroup in the Open Mobile Alliance (OMA), is a specification for the download of data contents in a mobile network. In the specification, a download descriptor is used to provide the information of media objects and download manners and options. A user agent downloads, according to the information in the download descriptor, the media objects through a radio http protocol. A user has to download a download descriptor based on the eXtensible Markup Language (XML) before downloading digital contents. Some attributes are defined in the download descriptor, according to which the user agent carries out download operations, e.g., the user downloads contents according to a Uniform Resources Identifier (URI) through the radio http protocol. The DLOTA provides such functions as capability matching at the user side, timing download, automatic download, resuming interrupted download, sending completion notification after the download process is completed, and so on. According to the functions, a generic method may be adopted to download contents of various types. Moreover, because the XML is used to implement the download descriptor, it is easy to extend the capability of the download descriptor by defining new attributes. In this way, the capabilities of a download agent and a download server may be extended according to new requirements to support new attributes without influencing existing operations.
Two download schemes are defined in the DLOTA specification:
Scheme 1: when downloading content, the user agent sends a download request to multiple download servers at the same time, and receives the content provided by a download server responding to the download request firstly.
Scheme 2: when downloading content, the user agent may send a request for downloading the content in chunk, which may implement pause and resuming of download process.
In Scheme 1, the download content is simplex and the download request may be sent to multiple download servers simultaneously, but the content may be downloaded from only one download server.
In Scheme 2, the pause and resuming of download process may be implemented, but because the download content is downloaded in serial, the total download time is not decreased.